STD tests look for bacteria, antibodies, antigens or other substances associated with various sexually transmitted diseases, including chlamydia, gonorrhea, hepatitis, herpes, HIV and syphillis. Tests can be done in a doctor's office, a medical clinic or at home with a lab kit. To find out more about how STD testing works, read our Guide to STD Tests and our expert interview with Tracey Powell and our interview with hepatitis b expert Chari Cohen.